<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
   <script>
     let score=Number(prompt('请输入你的分数'))
     if(score>=90){
        alert('A')
     }else if(score>=80 && score<90) {
        alert('B')
     }else if(score>=70 && score<80) {
        alert('C')  
     }else if(score>=60 && score<70) {
        alert('D')  
     }else{
        alert('E')
     }
   </script>
</body>
</html>